FUNGI.Several fungi have been isolated
from bumblebees. Known and suspected
pathogens include Paecilomyces farinosus, B.
bassiana, V. lecanii, M. anisopliae, Aspergillus
candidus, Hirsutellaspp., Acrostalagmusspp.,
Candida spp., Doratomyces putredinis and
Chrysosporium pannorum (cited by
MacFarlane et al., 1995, and Schmid-
Hempel, 1998). Fungi pathogenic to bumble-
bees can be distinguished by the colour of
their respective mycelia; P. farinosusis pale
yellow to orange; B. bassiana mycelium is
white; V. lecaniiis snow-white and C. panno-
rum is dirty yellow-white to brown.D. putre-
dinis is an apparent saprophyte that
produces dirty white mycelium that has a
strong, characteristic ammonia-like odour.
Fungal infections can cause overwintering
losses of queens. Furthermore, honey conta-
minated with yeast (Candidasp.) may be
unsuitable as stored nectar for bumblebees
(cited by MacFarlane et al., 1995).
PROTOZOA.Bumblebees are hosts to several
protozoans, including gregarines, micro-
sporidia and trypanosomes (MacFarlane et al.,
1995; Schmid-Hempel, 1998). The neogre-
garine Apicystis (formerly Mattesia) bombi
infects several species of bumblebees from
North America and Europe (Liu et al., 1974;
Lipa and Triggiani, 1996). Neogregarine
infection in Bombusis common, but disease
prevalence is low. Oocysts are ingested and
emerging sporozoites penetrate the midgut
wall and infect the fat body. Heavily infected
fat body is strikingly white but reduced in
size (Lipa and Triggiani, 1996). Normal fat
body is yellow to brown, depending on the
age of the queen (MacFarlane et al., 1995).
Microscopic examination for the presence of
oocysts is necessary to diagnose infection.
Oocysts are elongate with rounded ends and
measure 16–21μm long by 5μm wide in
fresh preparations. Oocysts in fixed and
stained preparations measure 11–14μm long
by 3.5–5μm wide (Lipa and Triggiani, 1996).
A. bombicauses premature death of bumble-
bee queens in spring.
The microsporidium Nosema bombiinfects
bumblebees from Europe, North America
and New Zealand. This pathogen affects
adult bees, developing primarily in the
Malpighian tubules. Infection extends secon-
darily to the midgut, tracheal matrix, con-
nective tissue and eventually the fat body
and occurs in larvae and pupae (MacFarlane
et al., 1995; McIvor and Malone, 1995). Spores
measure 4.2–5.9μm by 2.1–3.5μm in
unstained preparations (McIvor and Malone,
1995). N. bombiisolated from Bombus ter-
restrisL. is less infective in Bombus lapidarius
(L.) and Bombus hypnorum(L.) but more viru-
lent, causing greater mortality and early
death in infected hosts of these two species
(Schmid-Hempel and Loosli, 1998). Natural
infections of N. bombihave no detectable
effects on colony performance but they are
correlated with an increased production of
sexuals, particularly males (Imhoof and
Schmid-Hempel, 1999). N. bombi-infected
bumblebees have distended abdomens, are
unable to mate successfully and excrete diar-
rhoea-like faeces. N. bombican be eliminated
from bumblebee colonies by treating them
with fumagillin (MacFarlane et al., 1995).
Although the microsporidiumNosema apis
is a pathogen of the honeybee Apis mellifera,
some reports suggest that N. apisis patho-
genic to several species of bumblebees, where
it is confined to the midgut of adult males
and workers (as cited in MacFarlane et al.,
1995). N. apisreduces the longevity of worker
honeybees and their ability to forage. The
effects of N. apis on bumblebees are expected
to be similar to those manifested in honey-
bees (MacFarlane et al., 1995). It is assumed
that there is little interaction between bum-
blebees and honeybees in nature, limiting the
opportunity for the dissemination of
microsporidian pathogens between them. In
rearing facilities, however, the potential for
pathogen dissemination may be increased if
honeybee pollen is used as food for rearing
bumblebee colonies or if honeybees are used
to stimulate bumblebee queens to start pro-
ducing brood (MacFarlane et al., 1995).
Two trypanosomes, Crithidia bombi and
Leptomonas sp., are found in bumblebee
intestines (MacFarlane et al., 1995). C. bombiis
a prevalent parasite of bumblebees in Italy
and Switzerland (Shykoff and Schmid-
Hempel, 1991a; MacFarlane et al., 1995). The
pathogen passes through the alimentary tract
and is occasionally excreted (Gorbunov,156 S. Bjørnson and C. Schütte